color of the day

color_of_the_day.py

#!/usr/bin/env python
# py3
"""
$ ./color_of_the_day.py -h
usage: color_of_the_day.py [-h] [--full-summary] days_in_future

Determines car color for future date.

positional arguments:
  days_in_future  Number of days in the future to determine color

optional arguments:
  -h, --help      show this help message and exit
  --full-summary  If supplied will also print all days leading up to the
                  supplied day
"""

import argparse
import sys

COLORS = [
    'Red',
    'Orange',
    'Yellow',
    'Green',
    'Blue',
    'Purple',
    'Black',
]


def color_of_the_day(days_in_future):
    """
    Through mystical and oft-forbidden incantations the car color
    being manufactured on a given day in the future is divined.

    Args:
        days_in_future (int) - Number of days in the future to
            predict the production color

    Returns:
        str - The production color for the given day in the future
    """
    # if the future date is low enough (within the first five days)
    # nothing special needs to be done so just take the color
    # straight-up
    if days_in_future < 5:
        return COLORS[days_in_future]

    # If dividing by a full week leaves us with with a remainder of
    # 5 or 6 we know we're on a weekend
    if days_in_future % 7 in (5, 6):
        return 'No Color'

    # If we made it this far we know that we're past a week,
    # we just need to know by how many (so that we can subtract
    # a corresponding number of weekend days)
    days_offset = days_in_future // 7 * 2
    adjusted = days_in_future - days_offset

    # Before we can return a color, though, we need to know whether
    # our colors need to roll over (if the target day in the adjusted
    # future exceeds the length of the colors list).
    if adjusted < len(COLORS):
        # No need to roll over so just return as-is.
        return COLORS[adjusted]

    # Rollover needed, adjust accordingly.
    adjusted = adjusted % len(COLORS)

    return COLORS[adjusted]


def main():
    # This stuff is housed in a function so my PEP8 linter
    # doesn't yell at me :(

    # Stupid simple arg parsing so why not.
    parser = argparse.ArgumentParser(
        description='Determines car color for future date.'
    )
    parser.add_argument(
        'days_in_future',
        type=int,
        help='Number of days in the future to determine color'
    )
    parser.add_argument(
        '--full-summary',
        dest='full_summary',
        action='store_true',
        help=('If supplied will also print all days '
              'leading up to the supplied day')
    )
    args = parser.parse_args()

    if not args.full_summary:
        color = color_of_the_day(args.days_in_future)
        print(color)
        sys.exit(0)

    # add 1 so the actual target day is included in the summary
    for day in range(args.days_in_future + 1):
        color = color_of_the_day(day)
        print(color)


if __name__ == '__main__':
    main()